I'm far from being an expert but if a team wants to protect a group they have to have eyes on the entrances at all times. To not disturb the peoples inside I'd post them outside. Those sick peoples peoples usually come in AFTER the services have begun. Unless you have a bomber in a burka in your community already in, you will see them coming but if you know most peoples in there you'll be well protected.... Unless of course one goes bunkers and that no one can prepare for.